Arado Ar 234

In late 1940, the Reich Air Ministry (German: Reichsluftfahrtministerium, abbreviated RLM) offered a tender for a jet-powered high-speed reconnaissance aircraft with a range of 2,156 km (1,340 mi). Arado was the only company to respond, offering their E.370 project, led by Professor Walter Blume.[2] This was a high-wing conventional-looking design with a Junkers Jumo 004 engine under each wing.

Arado estimated a maximum speed of 780 km/h (480 mph) at 6,000 m (20,000 ft), an operating altitude of 11,000 m (36,000 ft) and a range of 1,995 km (1,240 mi). The range was short of the RLM request, but they liked the design and ordered two prototypes as the Ar 234. These were largely complete before the end of 1941, but the Jumo 004 engines were not ready, and would not be ready until February 1943.[2] When they did arrive they were considered unreliable by Junkers for in-flight use and were cleared for static and taxi tests only. Flight-qualified engines were finally delivered, and the Ar 234 V1 made its first flight on 30 July 1943 at Rheine Airfield (presently Rheine-Bentlage Air Base).[3]

By September, four prototypes were flying. The second prototype, Arado Ar 234 V2, crashed on 2 October 1943 at Rheine near Münster after suffering a fire in its port wing, failure of both engines and various instrumentation failures. The aircraft dived into the ground from 1,200 m (3,900 ft), killing pilot Flugkapitän Selle.[4] The eight prototype aircraft were fitted with the original arrangement of trolley-and-skid landing gear, intended for the planned operational, but never-produced Ar 234A version.

Differences between the pair of four-engined Ar 234 prototype aircraft

The sixth and eighth of the series were powered with four BMW 003 jet engines instead of two Jumo 004s, the sixth having four engines housed in individual nacelles,[5] and the eighth flown with two pairs of BMW 003s installed within "twinned" nacelles underneath each wing. These were the first four-engine jet aircraft to fly. The twin-Jumo 004 powered Ar 234 V7 prototype made history on 2 August 1944 as the first jet aircraft ever to fly a reconnaissance mission, flown by Erich Sommer.[6]

The projected weight for the aircraft was approximately 8 tonnes (7.9 long tons; 8.8 short tons). To reduce the weight of the aircraft and maximize the internal fuel, Arado did not use the typical retractable landing gear. Instead, the aircraft was to take off from a jettisonable three-wheeled, tricycle gear-style trolley[7] known as a Bugradstartwagen (nosewheel takeoff-carriage in English, as-described in an Ar 234A Typenblatt factory drawing for the Ar 234 V8 prototype) and land on three retractable skids, one under the central section of the fuselage, and one under each engine nacelle. This central main skid beneath the fuselage was originally intended to fully retract into the fuselage with skid-bay doors enclosing it, and was originally shown in a 1942-dated Arado engineering drawing, under its overall E 370 airframe factory development designation, as intended to be made from a three-sided channel-section component, featuring a set of nine triple-beaded wooden rollers within the channel-section mainskid, for ground contact purposes.[8] However, as with the operational Messerschmitt Me 163B rocket fighter which used a landing skid, it was discovered that such a skid-format landing gear for the Ar 234A design's prototypes did not allow mobility after the end of the landing run, which would have left aircraft scattered widely over an airfield's acreage, unable to taxi off the runway without remounting every aircraft on a trolley for towing off the landing area. Erich Sommer himself once noted for late 20th-century television that the landing skid-equipped prototypes, when touching down on a wet-turf airstrip, had a landing run characteristic that "was like greased lightning" and "like [landing on] soap", from the complete lack of braking capability of the landing skid system.[9]

The RLM had already seen the promise of the design and in July had asked Arado to supply two prototypes of a Schnellbomber ("fast bomber") version as the Ar 234B. Since the original skid-equipped Ar 234A's fuselage design was very slender and filled with fuel tanks, there was no room for an internal bomb bay and the bombload had to be carried on external racks.

Arado Ar 234 B-2 nose in the original 13 glazed-panels design, at the Steven F. Udvar-Hazy Center.

Since the cockpit was directly in front of the fuselage, the pilot had no direct view to the rear, so the guns were aimed through a periscope, derived from the type used on German World War II tanks, mounted on the cockpit roof. The defensive fixed rear gun system intended for the Ar 234A's prototype series was generally considered useless – much like similar rearward-firing, fuselage mount guns placed on the fuselage of the first five prototypes of the Heinkel He 219 night fighter – and such fixed, rearwards-mount machine guns were omitted in production examples of the Ar 234B, while still retaining the periscope for rearwards vision. The external bombload, and the aforementioned presence of inactive aircraft littering the landing field after their missions were completed (as with the similarly dolly/skid-geared Messerschmitt Me 163) made the skid-landing system impractical, so the B version was modified to have fully retractable tricycle landing gear, with the mid-fuselage very slightly widened to accommodate the forward-retracting main gear units, the nosegear retracting rearwards. The ninth prototype, marked with Stammkennzeichen (radio code letters) PH+SQ, was the prototype Ar 234B, and flew on 10 March 1944.

Production B-series aircraft (like the Ar 234 V9) were slightly wider at mid-fuselage to house the main landing gear, with a central fuel tank present (the middle one of a trio of fuel tanks) in the mid-fuselage location on the eight earlier trolley/skid equipped prototype aircraft having to be deleted for the retracted main gear's accommodation. The 1942-executed engineering drawing of the trio of fuel tanks in the fuselage, when using a skid/trolley undercarriage design, showed a 1,430-litre (378 US gal) forward tank, the aforementioned central tank of some 830 litres (219 US gal) capacity, and an aft tank of 1,540 litres (407 US gal) capacity.[10] - the V9 and later examples had enlarged forward (1,800-litre/476 US gal) and aft (2,000-litre/528 US gal) fuel tanks to compensate for the omitted 830-litre central fuel tank.[11] Under tests with maximum bombload consisting of three SC 500 bomb, the Ar 234 V9 aircraft could reach 672 km/h (418 mph) at 5,000 m (16,000 ft).[12] This was still better than any bomber the Luftwaffe had at the time, and made it the only bomber with any hope of surviving the massive Allied air forces. The normal bombload consisted of two 500 kg (1,100 lb) bombs suspended from the engines or one large 1,000 kg (2,200 lb) bomb semi-recessed in the underside of the fuselage with maximum bombload being 1,500 kg (3,310 lb). If the war had continued it is possible that the aircraft would have been converted to use examples of the FuG 203 Kehl MCLOS radio guidance transmitter system to deploy and control one Henschel Hs 293 air-to-surface missile, itself weighing some 1,045 kg. The Hs 293 would have needed to be lengthened by 300 mm and be suspended at an angle in order to provide sufficient ground clearance. It could also carry the heavier BT 1400 (1,510 kg unpowered bomb-torpedo), although ground clearance would be very limited. In case the BT 1400 ordnance was to be deployed on an Ar 234B for an operational sortie, fuel had to be reduced, and the jettisonable Starthilfe Walter liquid-fueled rocket booster pods needed to be used for takeoff.

Production lines were already being set up, and 20 B-0 pre-production aircraft were delivered by the end of June. Later production was slow, as the Arado plants were given the simultaneous tasks of producing aircraft from other bombed-out factories hit during the USAAF's Big Week, and the ongoing license-building and nascent phasing-out of Heinkel's heavy He 177A bomber, even as the Arado firm was intended to be the sole subcontractor for the He 177B-series strategic bomber, meant to start construction at Arado as early as October 1944.[13] Meanwhile, several of the Ar 234 prototypes - including a few of the surviving six twin-engined Jumo 004-powered "trolley-and-skids" Ar 234A-series prototypes - were sent forward in the reconnaissance role. In most cases, it appears they were never even detected, cruising at about 740 km/h (460 mph) at over 9,100 m (29,900 ft), with the seventh prototype achieving the first-ever wartime reconnaissance mission over the United Kingdom by a Luftwaffe-used jet aircraft.

The few 234Bs entered service in autumn and impressed their pilots. They were fairly fast and completely aerobatic. The long takeoff runs led to several accidents; a search for a solution led to improved training as well as the use of twin HWK-built, jettisonable liquid fueled monopropellant Starthilfe pioneering RATO units, one mounted under each outer wing. The Jumo 004 engines were always the real problem; they suffered constant flameouts and required overhaul or replacement after about 10 hours of operation.

The most notable use of the Ar 234 in the bomber role was the attempt to destroy the Ludendorff Bridge at Remagen.[14] Between 7 March, when it was captured by the Allies, and 17 March, when it finally collapsed, the bridge was continually attacked by Ar 234s of III/KG 76 carrying 1,000 kg (2,200 lb) bombs. The aircraft continued to fight in a scattered fashion until Germany surrendered on 8 May 1945. Some were shot down in air combat, destroyed by flak, or "bounced" by Allied fighters during takeoff or on the landing approach, as was already happening to Messerschmitt Me 262 jet fighters. Most simply sat on the airfields awaiting fuel that never arrived.

Overall from mid-1944 until the end of the war a total of 210 aircraft were built.[2] In February 1945, production was switched to the C variant. It was hoped that by November 1945 production would reach 500 per month.

Ar 234B-2/N night fighter adaptation

In addition, it was intended to modify upwards of 30 Ar 234B-2 airframes for the night-fighting role, from a proposal dated 12 September 1944 between Arado director Walter Blume and Goering's top aviation technologist, Siegfried Knemeyer.[15] Designated Ar 234B-2/N and code named Nachtigall (Nightingale), these aircraft were fitted with FuG 218 "Neptun" VHF-band radar, with the appropriately reduced-dipole length version of the standard Hirschgeweih eight-dipole element, VHF-band transceiving AI radar antenna system, and carried a pair of forward-firing MG 151/20 autocannon within a Magirusbombe conformal gun pod on the ventral fuselage hardpoint. A second crew member, who operated the radar systems, was accommodated in a very cramped compartment in the rear fuselage. Two of these jury-rigged night fighters served with Kommando Bonow, an experimental test unit attached to Luftflotte Reich. Operations commenced with the pair of 234Bs in March 1945, but Bonow's team soon found the aircraft to be unsuited for night fighting and no kills were recorded during the unit's very brief life.

Two-view silhouette of basic Ar 234C design

The Ar 234C was equipped with four lighter-weight (at 625 kg/1,380 lb apiece) BMW 003A engines, mounted in a pair of twin-engine nacelles based on those from the eighth Ar 234 prototype. The primary reason for this switch was to free up the 720 kg weight Junkers Jumo 004s for use by the Me 262, but the change improved overall thrust to nearly 3.2 tonnes (7,040 lbf) with all four BMW jets at full takeoff power, especially useful for takeoff and climb-to-altitude performance. An improved cockpit design, with a slightly bulged outline for the upper contour integrating a swept-back fairing for the periscope, also used a much-simplified window design with far fewer glazing panels (8 in total), than the total of 13 separate glazing panels of the Ar 234B cockpit – itself taken almost unmodified in form from the eight A-series "trolley-skid" prototypes – for ease of production. The quartet of BMW jet engines gave the C-series Ar 234s an airspeed that was found to be about 20% higher than the twin-Jumo 004 equipped B series airframes, and the faster climb to altitude meant more efficient flight and increased range.

Although Hauptmann Diether Lukesch was preparing to form an operational test squadron, only 14 C-series airframes had been completed by the war's end, and of that number fewer than half had been fitted with engines, with a few of them found at the end of the war sitting out in the open, otherwise complete but with empty engine nacelles – only about 500 examples of the BMW 003 jet engine were ever built, with priority for their production going to the Heinkel He 162A Spatz emergency fighter's own production program. Comprehensive flight testing of the new sub-type had yet to begin when Germany surrendered. Three basic variants of the C-series were planned for initial construction, with several more laid out as detailed proposals. Some of these would have had a pair of the higher-thrust, but heavier (at some 950 kg/2,095 lb apiece) Heinkel HeS 011 jets for flight, while others were intended to feature swept or "crescent"-type wings.

The D model was a two-seat aircraft based on the B-series fuselage, but with a new, enlarged two-seat cockpit possessing fewer glazing panels than the C version, intended to be powered by a pair of more powerful Heinkel HeS 011 turbojet engines. The HeS 011 powerplant never reached quantity production, with only 19 examples of the new powerplants ever created for test purposes, and no 234D was produced, beyond a few wooden engineering mockups.

The P model was a two-seat night fighter version with a variant of the D-series cockpit, differing in powerplant options and several options of radar. Several were in the planning stage, but none made it into production.